So I was browsing the index here, and I noticed that there wasn't yet a build for a ship that I have some fond memories of piloting, the one ship that launched my entire career (if you can call it such) of healing in STO: the Deep Space Science Vessel. Clearly, this won't do; I shall take it upon myself to lovingly craft a fine --and cheap!-- build for this absolute gem of a vessel!

Nostalgia aside, the DSSV is actually a wonderful little ship for healing; I'd call it the best of the free Fed ships for that job. A link for the build is here; I'll go over the important stuff below.

If you've looked at my eng/sci oddy heal build, you'll very quickly notice that there are a lot of similarities between that build and this one. In particular, both place a very strong emphasis on good science heals; in fact, having the DSSV as my first healboat is the reason why I chose to put a high-level science officer on the oddy. Since such a large part of the build is shared (such as main healing tactics and escape buttons), I'll just note a few important differences.

1. Your hull is thin. Your shields are not.
The DSSV, like other science vessels, has a great shield mod in exchange for a thin hull. This means that effects that grant shield resistance, like RSF, EPtS, and TSS, can be put to great use, but that you also have to be extra-careful about taking hull damage. Any amount of hull damage is cause for concern while you're piloting the DSSV; the three neutronium consoles slotted will be helpful, but they cannot obviate the need for good tactics. This means that you must:

Pay close attention to how your shields are distributed. Use TT liberally if you're under fire, and be very, very careful during its 5s downtime -- if a shield facing goes down and they hit hull, you're liable to explode. In addition, the DSSV can turn moderately well; maneuver to present the strongest shield facing to your enemies.

Be wary of hull DoTs. Don't wait for too long before you hit the hazard emitters; you have two copies of them (of high ranks, to boot), so use them when you're being slammed by seven or eight plasma torpedoes all at once.

Be proactive with polarize hull. If you think that your shields are about to fail, or you're being roasted alive by plasma, use it! It's also great for escaping from tractor beams and thereby evading alphas.

On the flip side, your shields are able to soak up a lot of damage, especially if you attain high shield resistance. This will be your primary defense in normal combat; your survivability will depend on keeping your shields full and your shield resistance high. This means that you should:

Keep EPtS cycling, and integrate TSS into the cycle when you come under fire. This is more important than ever; without good shield resistance, your shields -- no matter how thick they are -- are going to evaporate under any sort of attack. TSS will be your standard shield heal if you come under focus fire, with EPtS providing the core resistance that keeps you going.

Use BFI often, possibly at the same time as other shield heals. With your shield distribution officers, BFI becomes a fairly reliable source of strong shield heals. But because your shield capacity is so high, don't expect BFI to completely fill your shields by themselves. Get comfortable using BFI in combination with other shield heals like EPtS and TSS.

Use RSF a little earlier. The strong shield resistance provided by RSF combos extremely well with high shield cap and will greatly extend the time that your shields stay up, but it can't save you if your shields are completely gone.

Thankfully, your Engineer captain abilities can help you make the most out of the strong shields, and help you patch up any holes you do take in the ship's thin hull.

2. AtSIF + Damage Control Engineers
The DSSV is a little low on the engineering heals, but the Damage Control Engineers really help fill the gap. Because the additional heal they provide is not tied to the rank of AtSIF used, they can provide a huge boost to the amount of healing that your AtSIF1 does. If they proc, they can easily cause AtSIF1 to heal as much as HE2, over a shorter period of time with a faster cooldown!

3. What to do with that Cm. Sci slot?
This is really up to you. Because there are no heals at Cm. Sci level, I don't have a strong recommendation for what should go on a healboat. I'd tentatively suggest PO3, just so you can get back on your feet quicker after you've been SNB'ed (or even chain-SNB'ed). Other useful alternatives include PSW in order to knock off enemy extends, or TBR to clear mine/torpedo spam.

Cost:
In terms of cost, this build is on the cheap side for PvP; free ship, no fleet gear, white (or nonexistent!) weapons, cheap/free doffs:

Rarities are suggested based on what I use currently. This level of gear can be bought from the exchange for very cheap.

VR Shield Distribution Officers can be obtained for free from criticals on the Rolor Nebula colonization repeatable mission.

The other doffs, being only rare quality, are likewise fairly cheap on the exchange.

The Photonic Displacer console was just given away as part of the Rhode Island Refit, so most people should have it. If not, then any other console of your choice may be substituted (preferably some sort of escape ability).

Photonic Officer 3 is rare, but if you ask in OPvP you might find someone willing to train it for you for free, since those that can obtain it have an infinite supply.

The biggest investment will be the reputation gear; the good news is that it's all from the Omega tree, and Mk X tends to work just as well for pug PvP as Mk XI or even Mk XII.

Final thoughts:
In summary, the DSSV is one of the lesser-known gems for healboating. Neglected and oft-maligned, it actually has a fairly strong bridge officer layout and good console slot distribution. I consider it the best free Fed ship for healing; while it may not be able to measure up directly to the Oddy or the Recluse, it's a great little workhorse that will serve you well until you decide to make the big investment into PvP healing. (Plus, it's fun to come back to even after you've gotten yourself one of those fancy ship!)

(Oh, and DDIS? Remember how you said that eng/sci had no real synergy at all? Well, you're wrong. )